WO1989008940A1

WO1989008940A1 - Process and circuit versions for charging accumulators

Info

Publication number: WO1989008940A1
Application number: PCT/AT1989/000027
Authority: WO
Inventors: Gerhard Wiesspeiner
Original assignee: Gerhard Wiesspeiner
Priority date: 1988-03-11
Filing date: 1989-03-10
Publication date: 1989-09-21
Also published as: ATE106631T1; DE58907791D1; EP0409847A1; AU3349789A; EP0409847B1; JPH07118868B2; US5256957A; JPH03500959A; AU630603B2

Abstract

Process for charging accumulators and circuit versions for implementing said process. The charging state of a 100 % charged accumulator is determined by measuring the extreme value of the variation of the charging parameter, e.g. maximum voltage, minimum current, or minimum resistance, with time. The time at which this extreme value is reached can be used to control the charging operation. The extreme value can be detected by means of electronic analog-digital or computer circuits. These circuits can be produced by discrete or hybrid technology and can be integrated on a monolithic substrate.

Description

Method and circuit variants for charging accumulators

The invention relates to a method for charging accumulators and possible circuit variants for its implementation.

State of the art:

The problem of charging batteries, in particular gas-tight Ni-Cd batteries, is known to the person skilled in the art, as is known to the users concerned. There is still a great need for simple and reliable battery charging circuits, especially for Sehnell charging. The difficulties in recognizing the optimal switch-off time to achieve full charging and protecting against overcharging are characterized in / 1 // 2 /. The well-known charging methods and circuits can also be seen in / 1 // 2 /. Recent inventions in this field (e.g. DE 3705222A1, DE 3440430A1, ...) relate to design variants or circuit details of these principles. It is characteristic of almost all circuits that the switch-off criteria of predefined values e.g. Final charge voltage, cell temperature or gradient, amount of charge, and the like. be derived.

Novelty:

The new invention differs from known methods in that it is not a specific value, but rather the time course of one or more charging parameters (voltage, current, internal resistance) that is detected and evaluated. With constant current charging, the voltage curve shows an increase before full charge is reached and then a decrease afterwards. A characteristic maximum arises. This fact was well known, but so far it has not been given the correct meaning. For example, in / 2 / circuit variants are presented that interrupt the charging process when the battery voltage drops during constant current charging.

The disadvantage of this method is that, in principle, an overcharging of the cells already occurs with a falling characteristic curve, and that reliable function is only provided for several gas-tight NiCd sintered cells connected in series, which must be precharged.

Reaching the maximum, however, characterizes the fully charged cell and is therefore an ideal criterion for controlling battery chargers, because this criterion is largely independent of the cell type, specimen spread, number of cells, temperature, parasitic voltage and environmental influences.

The maximum is caused by the electrode overvoltage during gassing. The subsequent voltage drop is caused by excess temperature and pressure and does not occur with open cells. The (current-dependent) voltage has reached a maximum end value that no longer increases (maximum) even through long-term energy supply. To protect against overcharging, it is therefore advisable to switch off the energy supply or to reduce it to an innocuous minimum when the maximum is reached, i.e. when the charging voltage stops rising. The rate of change becomes zero.

Equivalent statements regarding the occurrence of an extreme value when fully charged also apply to the course of the charging current (minimum) at constant voltage and the internal resistance of the cell (s). The patent application therefore describes inventions for controlling the energy supply when charging batteries to protect against overcharging and to prevent malfunctions caused by effects which are independent of the state of charge, as well as circuit variants and design variants for technical implementation.

Progress:

In addition to the already mentioned advantages of avoiding incomplete charging or overcharging, no additional sensors are required for the detection of the extremum and only a two-wire line is required to connect the battery. In addition, the same circuit arrangement can be used for different batteries and requires no adjustment in production.

This facilitates practical use and covers a wide range of applications.

Technical realization:

Methods for the detection of extreme values (minimum / maximum) are generally assumed to be known (analog, digital, computer) and can be found in the relevant literature.

Since the present case involves very slow processes with only very minor changes, it is advisable to use a microprocessor with ADC or DAC and comparator. In principle, however, all known circuits are possible which carry out a detection of the extreme value by differentiation, peak value measurement and difference formation, storage and comparison, or the like.

These circuits can be constructed from discrete components, as a hybrid or as a monolithic iC, or their function can be implemented by the program of an arithmetic unit (process computer, microprocessor).

According to the invention, this also creates the possibility for the first time of designing the entire control circuit for battery charging as an independent component with only three connections.

The basic mode of operation and function of the above-mentioned circuits and assemblies of electronics or the necessary programming technology are well known to the person skilled in the art, the use and arrangement of the same for the detection of an extreme value for optimal control (switch-off criterion) of battery chargers and the embodiment is new and was not obvious.

Another problem, especially with NiCd batteries, is the loss of capacity caused by the memory effect. In many cases, the battery can be "regenerated" by repeated charging and discharging. This process is very complex. By automating this manipulation there is a significant advantage for the user. The combination of several functions, in particular loading, with automatic capacity measurement and / or regeneration offers an additional advantage and progress. Literature:

/ 1 / General Electric: Nickel Cadmium accumulators.

Application technology manual of

General Electric Plastics GmbH,

Ruesselsheim, 1975

/ 2 / Retzbach, Ludwig: Batteries and Chargers,

Model reference book ISBN3-7883-0142-2, Vilbig Verlag, 1985

Detailed description of the inventions:

The battery voltage is determined by various mechanisms.

1. Electrode cell potential Uo (pressure and temperature dependent) 2. The electrode overvoltage (current and charge state dependent) 3. The internal resistance

Accordingly, there are 4 charge status ranges (A-D)

A. Accu empty: high internal resistance

B. Medium state of charge

C. Accu full: electrode overvoltage increases, gassing begins.

D. Overcharge

Fig.1a) shows the simplified equivalent circuit diagram of the battery.

The internal resistance is in series with the cell voltage Uo. The internal resistance is composed of a portion Rv that characterizes the uncharged battery and the internal resistance Rii that characterizes the fully charged battery. The capacitor C, which acts in the center of the partial resistors and lies parallel to Rii and the cell voltage, allows both partial resistors and their behavior to be detected by changes in current or voltage or in their AC components.

This can also be used to calculate the internal battery voltage (Ui), which describes the charge more accurately than the clamping voltage between the anode and the like. Cathode.

The current-voltage change that may be required is at least always given at the time of switching on. Fig.1b) shows the time course of the battery voltage Ua and charging current I with the associated rates of change dU / dt and dl / dt.

During the charging time t, the battery voltage increases until a final value is reached, whereas the charging current decreases. When the maximum of the charging voltage (Ua) or the minimum of the charging current (I) is reached, the rate of change (dU / dt, dl / dt) approaches zero.

Since, in particular with the open cell, there is no pronounced extreme value, but a creeping extreme value, with the rate of change going very slowly towards zero, it is better to set a threshold for the minimum value of the rate of change at which the cutoff or the reduction of the charging current he follows.

1c) shows an implementation variant for the charging method, in particular according to claim 1.

Circuits for measuring charging current and battery voltage supply the arithmetic circuit with measurement-dependent f (U), f (I) signals. These are linked in the arithmetic circuit and an auxiliary variable (S) is formed. The common trend of the voltage and current profile (for example R = U / I) or the voltage drop across the internal resistance or the voltage change when the current changes should and should preferably be taken into account in the arithmetic circuit. From this instantaneous value (S), which changes over time, the rate of change can be determined, for example, in a differentiator (dS / dt) or by storage and difference formation. If the change (dS / dt) in the instantaneous value (S) becomes smaller than the setpoint, the charging current is interrupted or reduced.

1d) shows another possible embodiment in digital or microprocessor technology.

The battery voltage (Ua) and the charging current, which also occurs, for example, as a voltage drop (Um-Ua) at a current measuring resistor (Rm), are sampled at certain times (delay time), digitized and possibly converted to size S1 and stored. After the delay time, size S2 is calculated in the same way. If the rate of change, characterized by the difference between (S2-S1) and the delay time, is below a comparison value, the charging current switch is actuated.

Fig. 2. shows circuit variants with constant current charging.

In contrast to known methods, the present invention switches off as soon as a minimum rate of increase in the battery voltage is no longer reached and not in the falling part of the voltage curve (FIG. 2a). Because the current is known for constant current charging, there is no need to measure it and it is sufficient to evaluate the rate of rise of the battery voltage.

Fig. 2b

The circuit design is therefore reduced to a constant current source, which in the simplest case can only be formed from a series resistor, the charging current switch and the battery in the charging circuit. The measuring circuit (switch-off logic) consists of the voltmeter whose output signal is fed to a differentiator. The charging current switch remains closed only as long as the output signal of the differentiator is above a reference value (setpoint) 1.

When controlling the power source itself, the circuit breaker can be saved (Fig. 2c).

Fig. 2c

The power source is connected directly to the battery. The retentive logic mentioned above taps the battery voltage curve and controls the power source.

When using a microprocessor with AD converter, which replaces the switch-off logic and controls the current source, it is also possible, as already described, to determine the components of the battery replacement circuit diagram by known variation of the current (FIG. 2D). 3 shows an embodiment variant according to claim 3 with constant voltage specification

The shutdown logic is in series between the voltage regulator and the battery. It contains a current transformer whose output signal is fed to a differentiator. The differentiated signal is fed to a comparator which opens the internal switch located in the main charging circuit and thus interrupts the charging current when the value falls below the comparison value.

The charging current tends to a minimum and di / dt approaches zero, which triggers the shutdown. (Fig.3a).

When switched on, the voltage regulator specifies the charging voltage, which therefore no longer has to be measured. The current measurement can include again as a voltage drop across a resistor. The shutdown logic can e.g. can be realized in a known manner from differentiators or with a microprocessor. (Fig.3b).

Fig. 4. Charge with pulsating current:

For the sake of simplicity, rechargeable batteries are only very frequently charged with pulsating current, such as that which arises from the rectification of the AC mains voltage.

By using a pulsating current, however, there are several advantages that have not previously been used. Since the time constant T = Rii * C (FIG. 1) is very high, the internal resistance Rvi = Uw / Iw can be determined, for example, from the ratio of the alternating voltage amplitude and alternating current amplitude. (Fig. 1) and calculate the internal stress using U; = Ug-Ig * Rvi * Ui (Fig.l). With increasing charge, the resistance Rvi shows a decreasing tendency while the resistance Rii increases and strives for a limit value (maximum) which characterizes the full state of the battery.

4 a, b show a profile of the battery voltage (Ua) and the charging current I with the pulsating alternating components (Uw, Iw) and the slow components (Ug, Ig) for trend detection.

The high internal resistance (Rvi) at the start of charging leads to a falling characteristic curve of the average battery voltage (Ug) and, if not taken into account, can lead to possible malfunctions for the detection of the switch-off time.

According to the invention, the method for taking these and other disruptive influences into account separates the DC (Ug, Ig) and AC components (Uw, Iw) from charging current I and battery voltage (Ua) by means of suitable circuits, such as differentiators and integrators or pulse-synchronous scanning, or digital arithmetic units, which can be processed together (FIG. 4c) or separately 4c. 4c shows a circuit variant.

There is a current measuring circuit in the charging circuit, such as. a current transformer which feeds the exchange component (Iw) and the DC component (Ig) to a computing circuit via a high-pass filter from the charging current-dependent signal f (I). The battery voltage is also measured f (Ua) and fed separately to the arithmetic circuit by low and high pass filters into a constant f (üg) and an alternating component f (Uw). The internal battery voltage is continuously calculated in the arithmetic circuit and compared with the switch-off criterion, and depending on this, the charging current is interrupted or reduced. 5th

A simplification of the technical implementation according to FIG. 4 can be achieved if the pulsating direct current is rectified by rectification from the mains alternating voltage and is zero in the current minimum. The voltage measured at this point in time is then equal to the internal cell voltage (Ui) due to the lack of voltage drops across the internal resistances of the battery (Rvi) and supply line.

5a shows an implementation variant.

In the simplest case, the constant current is obtained from the constant mains alternating voltage by means of a series resistor Rv. From the ripple of the battery voltage, the minimum of the individual pulses (U min) is filtered out by means of a peak value detector (e.g. analog circuit, synchronous sampling, digital pattern analysis, etc.) and fed to the switch-off detection logic. which in turn controls the charging current holder. 6.

Gassing in the event of overcharging is prevented if the internal battery voltage Ui remains below a predetermined value. The known constant voltage charge is not particularly suitable for this because, among other things. the voltage drop across various internal resistances is not taken into account. According to the invention, a remedy is created by determining the internal battery voltage (Ui) and comparing it with the setpoint value and, depending on this, adjusting the current in such a way that the internal battery voltage is regulated to the predetermined value.

Fig.6a. shows as an example the regulated internal battery voltage (Ui) measured at zero current.

Fig. 6b. shows the principle of operation of the method. using the example of a variant.

A controllable power source, e.g. a switching regulator feeds the battery. The battery voltage (Ua) is measured and the internal battery voltage is determined using the known current profile (fl). If there is a deviation from the setpoint, the current is adjusted accordingly.

7.

In many cases it is desirable to charge batteries of different capacities with an optimal charging rate. Usually, the capacity must be known to which the charging current must be set by the user.

An automatic adaptation of the charging current to the cell capacity is achieved according to the invention when the rate of increase of the battery voltage or the internal battery voltage Ui (FIG. 1) is regulated by the current setting. Fig. 7. shows a possible solution. The rate of voltage rise on or in the battery is determined, for example, by differentiating the battery voltage and fed to a comparator, which adjusts the current so that the differentiated value corresponds to the predetermined target value.

8th.

With constant voltage charging of batteries in series connection, the charging voltage must usually be specified according to the number of cells. An automatic setting would be advantageous. This advantage can be realized according to the invention by first measuring the open circuit voltage and, starting therefrom, the charging voltage is increased in steps or continuously until a minimum current is established. An embodiment variant of the method is shown in FIG. 8.

A microprocessor compares the current flow (I) from a voltage source to the battery with a predetermined value. If the current is less than the setpoint, a higher voltage is set on the voltage regulator. When the current is reached, the process is ended and the voltage remains set.

9th

Parasitic effects occur during the charging process, which can lead to malfunctions of the automatic switch-off. According to the invention, logic consisting of function and decision elements of analog or digital computing technology prevents, for example, that in FIG a logical OR function forces the switch-on as long as the signals of the switch-off criterion or the battery minimum voltage detector, or the discriminator for brief voltage dips, or the trend detection logic for falling battery internal resistance, which are also connected to the input of the OR circuit, are not all logic zero are.

10th

Charging circuits usually require a large number of electronic assemblies, individual components and controllers which have to be adjusted. A large number of the methods, principles and circuit variants presented in this document can be implemented from a few semiconductor components which can be accommodated in a single housing and thus form a new, independent component of power electronics. 10a shows an example of a block diagram and FIG. 10b shows an embodiment in hybrid technology.

A single chip microcomputer, for example, is used as a measuring and Control logic, a power transistor Tr as charging current controller and an internal voltage supply VCI housed and functionally connected.

The power connections of the power transistor are led to the outside as an input connection for supplying energy and as an output for connecting the battery. In the simplest case, the reference ground can be removed from the housing or can also be supplied via a separate connection. Other connections can be made to signal the charging status, for example. The entire circuit is housed in a housing and thus forms an independent component. Another exemplary embodiment is shown in FIG. 10c. The entire circuit is integrated on a semiconductor chip and accommodated in a standard housing with only 3 pins. Again, several connections can be provided to output additional signals.

A further simplification for the user is obtained if, in addition to the charge control circuit, the rectifier and possibly a switching regulator are combined to form a module. Such a component can be designed with 4 connections and brings significant simplifications in the manufacture of battery chargers. (Fig.10d)

11. Regenerate

The regeneration of batteries requires repeated discharging and recharging.

According to the invention, this process is automated in that a sequence control MP alternately activates a charger or a charging circuit and charges the battery and then discharges it through a discharge circuit such as a current sink until a predefined discharge voltage is reached. Another feature of the invention is that this process is repeated as many times as the discharge capacity increases. The increase in the discharge capacity can be determined, for example, by measuring the discharge current over time or the discharge time for a given discharge current. A variant of this is shown in FIG. 11. 12th

Battery chargers should be versatile and universally applicable. The common arrangement of a charging and discharging circuit enables batteries to be checked for their function and capacity and, if necessary, regenerated. The display of the amount of electricity to be charged or removed in Ah or as part of the battery capacity is an important aid for the user.

The automatic adjustment of charging current and charging voltage also allows laypersons through the function selection via a keyboard, switch or the like. optimally charge, test or regenerate any batteries. 12 shows a possible embodiment variant. A microprocessor is programmed so that the charge circuit or discharge circuit, which act jointly on the battery connection terminals (plug or the like), are activated functionally at the push of a button. The current is continuously recorded via a current measuring circuit, calculated in the MP and shown on a display. 13th

Production and aging-related batteries have different capacities. The amount of electricity that can be stored is limited in series by the capacity of the worst. If the capacities are unequal, reversal of polarity and irreversible damage to the weakest occur when the battery is completely discharged. A single switch-off interrupts the current flow of the whole series connection and the other battery capacity is also lost.

According to the invention, therefore, not a switch but a switch is provided which takes the battery out of the series connection when fully charged or discharged and switches to a bypass line, so that the Circuit of the series circuit remains closed. The switch is operated by a switching logic that works depending on the charge level of the battery. Fig. 13

14th

Easiest use and highest reliability of accumulators is achieved if the above Circuit protects each accumulator and is not a separate component. Due to the size of batteries and electronic circuits, the possibility of installation or addition is beyond doubt.

Claims

Expectations

1 . Processes, devices and circuit variants for charging, in particular Sehnell charging, of accumulator batteries, in single or series connection, in which the energy supply is switched off or reduced to prevent overcharging, and the main criterion for switching off is the time The course of charging current and battery voltage is used, these signals being measured automatically or one of the two being predetermined in a known manner, characterized in that the rate of change is automatically converted from a parameter which can be derived from the measured variables into a signal which can be evaluated by measurement and control technology, and a comparison operation is supplied, which subsequently causes a shutdown or reduction of the energy supply if the size of this signal is below a predetermined minimum value.

2. The method, devices and circuit variants according to claim 1, characterized in that the battery is supplied with a constant current and the increase in time of the charging voltage is converted into the signal for triggering the switching process.

3. The method, devices and circuit variants according to claim 1, characterized in that the charging voltage is predetermined and the decrease in time of the charging current is converted into the signal for triggering the switching process.

4. The method, devices and circuit variants for charging rechargeable batteries characterized in that the battery is supplied with the energy in a pulsating manner, on the one hand the pulsations for detecting the switch-off criterion are filtered out and on the other hand automatically an additional, related to the internal resistance of the charging circuit, from the measurement of the pulsative current voltage change, Signal is derived, which in particular allows a conclusion to the internal line voltage or contact errors and in turn influences the switching process correcting or superordinate.

5. The method, devices and circuit variants according to claim 4 particularly characterized in that the battery is supplied with a pulsating direct current and the course of the battery voltage is measured at zero current or in the current minimum of the individual pulses.

6. The method, devices and circuit variants according to claim 4 particularly characterized in that by changing the pulsating charging current, the battery voltage, preferably the internal battery voltage, is regulated to a predetermined target value and the course of the average charging current causes the switching process, for example in claim 3.

7. The method, devices and circuit variants for charging accumulators, characterized in that a control device regulates the rate of increase of the accumulator voltage or the internal accumulator voltage by setting the charging current to a value specified by a reference variable.

8. The method, devices and circuit variants for automatically setting the charging voltage of batteries, characterized in that a control circuit increases the voltage of a voltage source for as long until a signal derived from the charging current is greater than a predetermined comparison value.

9. The method, devices and circuit variants according to claim 1, 2, 3, 4, particularly characterized in that a switching logic prevents the switch-off when the battery voltage or the decrease in internal resistance is below a predetermined value or when brief voltage drops occur.

10. Embodiment of control circuits for charging accumulators consisting of at least one detection logic for determining the switch-off time connected to an actuator for limiting the charging current to protect against overcharging, characterized in that the entire functional group is designed as a single component.

11. The method and circuit variants for regenerating the battery capacity by repeated charging and discharging, characterized in that a sequence control executes this process automatically and preferably repeats as long as the battery capacity increases.

12th

Device for the controlled charging and discharging of rechargeable batteries characterized in that the respective function of charging or discharging is switched on via a command input unit, such as a keyboard, and the supplied or removed amount of current or energy, or a quantity related to it, automatically measured by suitable circuits , is preferably displayed numerically and in electrophysical units or as a percentage of the battery capacity on a display and or additionally with a sequence control for automatic Regenerating the battery is preferably equipped according to claim 11, and or is equipped with circuits which automatically adapt the charging current and or the charging voltage to the respective battery.

13th

Circuit arrangement for charging accumulators with an automatic switch to protect against overcharging or complete discharge or incorrect polarity, characterized in that an automatic switch partially or completely disconnects the current path through the battery from a pole of the battery and bypasses the battery to a secondary current path or switches redirects to the other pole of the battery.

14th

Accumulator with protective circuit and embodiment of the

Circuit arrangement according to Claim 13, characterized in that the circuit is installed in a storage battery or battery pack or is structurally connected to it.

15th

Methods and circuit arrangements for operating batteries in

Series connection characterized in that single cells or groups of single cells with circuits according to claim

13 or designs according to claim 14 can be connected in series.